Which concept of a new front wheel can improve comfort?

By studying different competitor wheels during the benchmarking, it was found that they were performing overall the same. Also, all competitor wheels, as well as Thules two wheels, were constructed the same (see Figure 10). By looking at inspiration pictures, the idea of design a stroller wheel with more flexible material was a starting point. After completed brainstorming, some ideas were decided to continue working with as different concepts. Further, all concepts were modeled in CAD software and build as prototypes.

All concepts were then evaluated by the test method and rated in Pugh’s matrix. The result of the test method shows that Concept 3 performs better than the original Thule Chariot CAB wheel, and therefore, it is a wheel with improved comfort. However, when Concept 3 is rated in Pugh’s matrix, it seems to be worse at other important requirements. Especially the requirement “Radial stability.” If this requirement remains unfulfilled, Concept 3 won’t work.

Discussion and conclusions

6 Discussion and conclusions 6.1 Implications

This thesis work has resulted in an evaluation method, for how Thule Chariot CAB’s front wheel should be evaluated regarding increased comfort. The evaluation method that was done in this study is just one way to evaluate wheels, and was made since there is no existing method.

Further, a concept study was performed were several concepts were produced by purpose to improve the comfort of the stroller. Two concepts broke during the evaluation test. It may depend on that the 3D-printed material (PA12) is more brittle at hard impact or that the parts were under-dimensioned. However, one of the concepts that were produced resulted in improved comfort properties since its bounce height was lower than the original wheel when the wheels were evaluated. Because this study didn’t conduct the three latest step in the development phases, see 2.5 Product development, no one knows if Concept 3 will be able to be manufactured or not.

6.2 Conclusions and recommendations

The purpose of the study was to create an evaluation method for how Thule Chariot CAB’s front wheel should be evaluated regarding improved comfort. Further, a concept study was performed, where the goal was to achieve a stroller wheel that could contribute to increased comfort. With respect to the delimitations set in the project, both of the study’s question formulation considered to be fulfilled.

- How shall Thule Chariot CAB’s front wheel regarding comfort improvement be evaluated?

Thule Chariot CAB’s front wheel is evaluated regarding improved comfort by IrregularST and its association to real life use as described in theory 2.3 Connection between Thule's customers and IrregularST. The evaluation method for increased comfort is defined in the study as a wheel that decreases the bounce height.

- Which concept of a new front wheel can improve comfort?

One of the concepts that were produced contributed to improved comfort since its bounce height was lower than the original wheel. However, it is lacking on other requirements which need to be processed in order to make the wheel working.

6.3 Future work

Since two concepts broke down and it could depend on the 3D-printed material, they could be redesigned and re-tested. Anyhow, if Concept 3 is further developed which performed best in the evaluation method for improved comfort, the remaining requirements must be processed.

In particular, the stabilization of the wheel in the radial direction has to be improved. The wheel also needs to undergo several other tests as statically loaded, for example, to ensure that the soft material in the center does not change over time, which would lead to an uneven rolling. I consider that the difference between Concept 3 and the original Thule Chariot CAB wheel isn’t sufficiently noticeable to gain something of it, at least according to my evaluation method.

Therefore, Thule needs to investigate more about what is comfort and how it should be evaluated properly in order to strengthen the argument for which wheel that is good or not. A reduction of vibrations during whole-body-vibration testing could be an alternative evaluation method for improved comfort, similar test as the automotive industry does on their products.

6.4 Reliability and Validity

The study’s reliability and validity are various. Because comfort includes so many parameters, the experimental analysis performed in this study considered as acceptable. In order to increase the validity of the evaluation method, this quantitative data (measured numbers) should be compared with qualitative data (interviews and personal experience) The evaluation method measures the bounce height when the wheels are run at IrregularST. Because of the standard test, IrregularST is used, the study considered to have good reliability. The test can always be

performed with the same precision again, since the speed of the treadmill, the obstacles and the surrounding are the same.

In order to strengthen the concept study’s validity, well-proven methods like QFD and Pugh were used. To increase the concept study’s reliability, the requirements weighting factor (QFD) was decided together with engineers at Thule. The same procedure was done when the concepts were eliminated by Pugh’s matrix. Also, the wheels were tested by the evaluation method to evaluate the first requirement, which increases the reliability of Pugh’s matrix execution.

Measuring the bounce height using only the maximum acceleration can be seen as poor reliability. However, reliability is strengthened because the wheels are video recorded. The fact that the study uses a non-calibrated measurement tool impair the study’s reliability. Since the study does not seek any specific values but only a difference, the phone’s accelerometer considered as acceptable.

6.5 Project reflections

To improve Thule Chariot CAB’s comfort characteristics by examining whether or not it’s possible to improve the front wheel is something completely unfamiliar for Thule. One challenge has been to decide how much time different stages of the project is going to take. The consequence is, for example, that the concept generation phase has to hasten, because the test machine (IrregularST) in Thule’s test center is booked a certain time.

If the work has been remade with the knowledge obtained today, it would maybe be better if only one question had been conducted. As a suggestion, it would have been good to decide what Thule’s customer think is comfort concerning all its parameters and not just the bounce height.

References

References

[1] Thule Group AB, “thulegroup.com” Thule Group AB. [Online].

Available: https://www.thulegroup.com/en/about-thule-group [Retrieved: 12 December, 2018]

[2] Swedish Standards Institute (EN). (2019). Child care articles – Wheeled child conveyance – part 1: Pushchairs and prams. (SS-EN-1888-1:2019). Stockholm, Sweden: SIS

[Retrieved: 15 April, 2019]

[3] Heida International, ”heidatestequipment.com” Heida International, [Online].

Available: https://www.haidatestequipment.com/products/uneven-road-stroller-test-equipment.htm

[Retrieved: 15 April, 2019]

[4] J. Rosengren, “Evaluation and verification of dynamic requirements for strollers,”

LUP Students Papers, vol. 2018, August 2018. [Online].

Available:

http://lup.lub.lu.se/luur/download?func=downloadFile&recordOId=8956485&fileOI d=8956489

[Retrieved: 5 March, 2019]

[5] J. M. L. K. J.N. Bolton, Engineering Mechanics Dynamics, 8 ed., Willey: 2016, pp. 174 [6] H. J. J. -G. P. Dennis Pettersson, Produktutveckling – Effektiva metoder för

konstruktion och design, 2 ed., Stockholm: Lieber AB, 2013, pp. 115.

[7] Allied Packing & Rubber, “alliedpackingandrubber.com” Allied Packing & Rubber.

[Online]

Available: https://www.alliedpackingandrubber.com/index.php/products/rubber-sheets-stripping/epdm-sheet-rubber/epdm-sheet-80-durometer-black-sheet-detail [Retrieved: 28 May, 2019]

[8] Elastocon, “elastocon.se” Elastocon Testing with precision. [Online]

Available:

https://elastocon.se/index.php/sv/component/virtuemart/gummi/mekanisk-provning/hardhetsmatare?gclid=Cj0KCQjwitPnBRCQARIsAA5n84k9oscWcUhTQX9 nNN7pUWQRfErycGlhtOnBEnjN1FPHLX88hfl6K5oaAiZHEALw_wcB

[Retrieved: 28 May, 2019]

[9] Naturskyddsföreningen, “naturskyddsforeningen.se” De vanligaste plasterna och tillsatsämnena, [Online]

Available: https://www.naturskyddsforeningen.se/node/35087/#B [Retrieved: 1 June, 2019]

[10] Omnexus, ”omnexus.specialchem.com” Omnexus The material selection platform [Online]

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[12] K. Österlin, Design i fokus – Varför ser saker ut som de gör?, 4 ed., Stockholm: Lieber AB, 2016, pp 64.

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[14] R. B. Davidson, Forskningsmetodikens grunder – Att planera, genomföra och rapportera en undersökning, 4ed., Lund: Studentlitteratur AB, 2011, pp. 102-107

Appendices

Product/ market analys 4 2 4 2 100%

Benchmark (Test) 5 2 8 1 100%

QFD 7 1 8 1 100%

Koncept development 7 9 8 9 100%

Brainstorming 7 1 8 1 100%

Idea sketching 7 5 9 3 100%

CAD 8 6 8 5 100%

Mockups/ prototypes 13 3 13 4 100%

Koncept elimination 16 2 15 3 100%

Brainstorming elimination 8 1 8 1 100%

Test 16 2 15 2 100%

Stroller name Chariot CAB Sleek Geo Fox Priam

Generally Unit

Market price (Incl. fork) 72,17 - 64,39 119,95 55,95 USD

Wheel size 7,8" 8" 7,5" 8,5" 7,5" Inch

Tyre widht 34 36 34 34 34 mm

Weight 412g 328g 292g 366g 406g gram

Number of components (except bearings) 3 3 4 4 3 pcs

Durable surface contact material (rubber) YES NO NO YES YES

Absorbing material (EVA) YES YES YES YES YES

Rim material Plastic Plastic Plastic Plastic Plastic

Appendix 3. Brainstorming

Appendices

Appendix 4. Inspiration picture

Appendix 5. Idea sketching

Appendix 6. Damaged concept wheels

Appendices

Appendix 7. Benchmarking result

Appendices

Appendix 8. Testing result

Nel documento LA RETE A.C.S. SAN VITO P.T.O.F. PIANO TRIENNALE DELL'OFFERTA FORMATIVA TRIENNIO (pagine 44-50)